1. Field of the Invention
This invention concerns a wavelength division multiplex transmission system and communication device, and in particular, concerns defect-avoidance processing.
2. Description of Related Art
The current flow of technology for expansion of the capacity of optical communication systems may be broadly divided into time division multiplex (TDM) methods, and wavelength division multiplex (WDM) methods.
Here, in a WDM method, signals are modulated at, for example, 10 Gbps per channel. In each channel, signals modulated at different wavelengths are superposed by a four-channel WDM optical coupler (wavelength division multiplexer), and through transmission in a single optical fiber, transmission at 40 Gbps can be achieved. Compared with TDM methods, this WDM method has been regarded as superior due to its ease of upgrading, power division costs, ease of maintenance, and service flexibility.
In the case of WDM methods, a transmission signal is distributed among wavelength components for transmission, so that both the optical transmission device and the optical receiving device are provided with processing units accommodating each of the wavelength components. In the event that a defect occurs in any of the processing units accommodating a wavelength component, ordinary transmission will no longer be possible.
For this reason, it has previously been proposed that a redundant configuration of an operating system and standby system be employed, together with an optical transmission device and optical receiving device.
However, even if a redundant configuration is adopted, transmission is not possible when defects occur in both the operating system and the standby system. In order to avoid this phenomenon, provision of a plurality of standby systems is conceivable. However, in this case the equipment size is increased, so that practical accommodation is not possible.
In general, when a defect occurs in the operating system, the standby system is used in transmission, and while this standby system is being used, the operating system is restored to the normal state by replacement of parts or by other means. However, if there is a long length of time from occurrence of the defect until replacement of parts or similar in the operating system, the possibility of a defect occurring in the standby system during this interval is increased. Consequently, shortening of the time until part replacement is desired.